With the advent of low cost computers, musicians sought a way to use a computerized system to capture data representing the keys played by a musician on an electronic keyboard as an electronic representation of music much like a printed score. The most common format for such data representing music is "MIDI", an acronym for musical instrument digital interface. Because the electronic keyboard generates an electric signal when each key is pressed, MIDI data can be generated from such a keyboard instantaneously so that the MIDI data can then be used to drive synthesizers to instantaneously produce desired music.
Musicians also want to use other sources to generate musical data, such as guitars, non-electronic instruments, and the human voice. Analog and digital circuits, including computer software methods on a general purpose computer, for determining the primary pitch or fundamental frequency of a musical source are well known. However, most of them do not have a quick enough response time to be used for generating sound from a synthesizer while the musician is playing and giving to the musician immediate feedback with the synthesized sound. Because of the lag time of processing, such systems are mostly used for creating musical data recordings or, with a lag from the original music creation, displaying on a computer screen a score which represents the music. These systems use methods involving the detection of either peaks at the highest and lowest values of the signal or zero crossings at the midpoint of the signal and measuring time durations between these events to determine the fundamental frequency. Recently, Roland Corporation has developed an improved high speed signal processing circuit for determining the primary pitch of each of numerous guitar strings and producing musical data with a short delay. However, because the circuits are optimized to operate quickly, the data output often contains errors which will cause the sound synthesizer to generate the incorrect sound, and further reduction in the delay is still desired.